This invention relates to an improved method and apparatus for TIG welding, more particularly to a method and apparatus for TIG welding of base metals by using a plurality of electrodes.
Generally, in a TIG (Tungsten Inert Gas Arc) welding method a tungsten electrode is projected from the tip of a welding torch toward a weld zone of a base metal, and the welding torce ejects an inert gas such as argon or helium to form an inert gas shielding atmosphere in which an arc is produced between the electrode and the base metal, whereby weld penetration of the base metal is achieved and a filler wire is fed from the tip of the welding torch and melted. In the above described welding method, since both the base metal and filler wire are melted by the arc produced by only one tungsten electrode, if welding heat input to the weld zone is excessive, the temperature of the molten pool in the base metal generated by arc heat is excessively increased and the base metal around the molten pool is also melted, resulting in serious problems in that the molten pool is expanded and molten metal tends to run out of it. Those problems are particularly liable to occur in welding a vertically positioned base metal. On the other hand, if the welding heat input is insufficient, the temperature of the molten pool drops, resulting in defective welding due to incomplete weld penetration. Therefore, in the conventional TIG welding method, since only one electrode serves the two functions of melting the filler wire and performing weld penetration, in order to avoid running away of melted metal, it is necessary to conduct the two functions under optimum conditions at all times for achieving sound welds. However, since it is difficult to maintain the optimum welding conditions at all times, increase of welding efficiency cannot be achieved.